Evolution of luminance by voltage in organic light-emitting diodes

We study degradation behaviors of luminance and voltage in organic light-emitting diodes. We find that normalized luminance and inverse normalized voltage with time, L(t) and V(t)^-1, follow the stretched exponential decay. On this basis, we derive a general relation of luminance and voltage with time as L(t)=V(t)^-δ(t), where δ(t) indicates a decay exponent, which is attributed to time-dependent space-charge limitation. Here the observation of higher δ(t) at higher initial luminance explains why luminance decay is faster at higher initial luminance.